Silencing of HIF-1 in WSSV-infected white shrimp: Effect on viral load and antioxidant enzymes

Hypoxia inducible factor-1 (HIF-1) is a transcriptional factor that induces genes involved in glucose metabolism. HIF-1 is formed by a regulatory α-subunit (HIF-1α) and a constitutive β-subunit (HIF-1β). The white spot syndrome virus (WSSV) induces a shift in glucose metabolism and oxidative stress. HIF-1α is associated with the induction of metabolic changes in tissues of WSSV-infected shrimp. However, the contributions of HIF-1 to viral load and antioxidant responses in WSSV-infected shrimp have been not examined. In this study, the effect of HIF-1 silencing on viral load and the expression and activity of antioxidant enzymes (superoxide dismutase-SOD, glutathione S-transferase-GST, and catalase) along with oxidative damage (lipid peroxidation and protein carbonyl) in tissues of white shrimp infected with the WSSV were studied. The viral load increased in hepatopancreas and muscle after WSSV infection, and the accumulative mortality was of 100% at 72 h post-infection. The expression and activity of SOD, catalase, and GST decreased in each tissue evaluated after WSSV infection. Protein carbonyl concentrations increased in each tissue after WSSV infection, while lipid peroxidation increased in hepatopancreas, but not in muscle. Silencing of HIF-1α decreased the WSSV viral load in hepatopancreas and muscle of infected shrimp along with shrimp mortality. Silencing of HIF-1α ameliorated the antioxidant response in a tissue-specific manner, which translated to a decrease in oxidative damage. These results suggest that HIF-1 is essential for restoring the antioxidant response, which counters the oxidative injury associated with WSSV infection.

Regulation of lactate dehydrogenase in response to WSSV infection in the shrimp Litopenaeus vannamei

Lactate dehydrogenase (LDH) is key for anaerobic glycolysis. LDH is induced by the hypoxia inducible factor -1 (HIF-1). HIF-1 induces genes involved in glucose metabolism and regulates cellular oxygen homeostasis. HIF-1 is formed by a regulatory α-subunit (HIF-1α) and a constitutive β-subunit (HIF-1β). The white spot syndrome virus (WSSV) induces anaerobic glycolysis in shrimp hemocytes, associated with lactate accumulation. Although infection and lactate production are associated, the LDH role in WSSV-infected shrimp has not been examined. In this work, the effects of HIF-1 silencing on the expression of two LDH subunits (LDHvan-1 and LDHvan-2) in shrimp infected with the WSSV were studied. HIF-1α transcripts increased in gills, hepatopancreas, and muscle after WSSV infection, while HIF-1β remained constitutively expressed. The expression for both LDH subunits increased in each tissue evaluated during the WSSV infection, translating into increased enzyme activity. Glucose concentration increased in each tissue evaluated, while lactate increased in gills and hepatopancreas, but not in muscle. Silencing of HIF-1α blocked the increase of LDH expression and enzyme activity, along with glucose (all tissues) and lactate (gills and hepatopancreas) concentrations produced by WSSV infection. These results demonstrate that HIF-1 up regulates the expression of LDH subunits during WSSV infection, and that this induction contributes to substrate metabolism in energetically active tissues of infected shrimp.

HIF-1α and PPARγ during physiological cardiac hypertrophy induced by pregnancy: Transcriptional activities and effects on target genes

Hypoxia inducible factor 1-α (HIF-1α) and peroxisome proliferator-activated receptor γ (PPARγ) are transcription factors that activate genes involved in cellular metabolism. Physiological cardiac hypertrophy induced by pregnancy initiates compensatory changes in metabolism. However, the contributions of HIF-1α and PPARγ to this physiological status and to its reversible, metabolic process (postpartum) in the heart are not well-defined. Therefore, the aim of the present study was to evaluate the transcriptional activities of HIF-1α and PPARγ in the left ventricle of rats before, during, and after pregnancy. Furthermore, the effects of pregnancy on target genes of glycolysis and glycerol-lipid biosynthesis, key regulatory enzymes, and metabolic intermediates were evaluated. The activities of HIF-1α and PPARγ increased 1.2- and 1.6-fold, respectively, during pregnancy, and decreased to basal levels during postpartum. Expressions of mRNA for glucose transport 1 (GLUT1), enzymes of glycolysis (HK2, PFKM, and GAPDH) and glycerol-lipid biosynthesis (GPAT and GPD1) increased 1.6- to 14-fold during pregnancy and returned to basal levels postpartum. The increase in GPD1 expression translated to an increase in its activity, but such was not the case for GAPDH suggesting that post-translational regulation of these proteins is differential during pregnancy. Glycolytic (glucose, lactate, and DHAP) and glycerol-lipid biosynthesis (G3P and FFA) intermediates increased with pregnancy and were maintained postpartum. The results demonstrate that pregnancy-induced, physiological cardiac hypertrophy activates the expression of genes involved in glycolytic and glycerol-lipid biosynthesis suggesting that the shift in cardiac metabolism is mediated by the activation of HIF-1α and PPARγ.